The inventions described herein relate to crystal oscillators. Although basic crystal oscillator arrangements are known, there is an unfilled need for an ultra-low power crystal oscillator, particularly for applications in battery-powered equipment to prolong battery life. For example, in personal computers, chip sets performing the function of a real time clock (RTC) must run on battery power when the computer is shut off and unplugged from a power outlet. It is desirable that a RTC chip set be able to operate for at least seven years on a factory-installed battery. For this purpose, a RTC chip set should consume less than 2 μA of current when running on battery power. When running on battery power, most of the power consumed by a RTC is consumed by its crystal oscillator. Typically, a crystal oscillator for a RTC operates at a rate of about 32 KHz and has a substantial “swing” which causes the oscillator to consume a significant amount of power. Various circuit arrangements of low power crystal oscillator circuits have been attempted. However, typically, they draw 6 μA amps or more of current making them unacceptable for many applications.
What is needed, therefore, is a crystal oscillator for a RTC chip set that consumes less power than a typical RTC so that devices that are battery powered can operate a substantial amount of time without the need to replace a battery.